This invention relates in general to chucks and in particular to a new and useful power chuck including setting pistons which act on drive members for displacing individual chuck jaws with uniform pressure to permit uniform chucking of the workpiece.
Power chucks are known in numerous designs and have proved satisfactory in practice. The drive members are provided in the shape of wedge bars, wedge hooks, toggle levers, or similar intermediate elements through which a movement of a connecting rod or a piston is mechanically transmitted to the jaws. In this way, all the jaws of a chuck are displaced through the same radial distance during a chucking operation, so that in every instance a centric outside or inside chucking is obtained.
Further known, from German OS No. 30 00 416, is a power chuck permitting not only a centric but also a balanced chucking. For this purpose, the jaws which are displaceable by means of a spring loaded setting bolt provided with a taper strip engaging the jaw, are equipped with chucking bolts which are inserted therein and project radially inwardly or outwardly beyond the jaw. Each chucking bolt is associated with a balancing hydraulic piston and cylinder. The cylinder spaces of the balancing cylinders communicate with each other through flexible tubes and form a closed hydraulic system which is adjustable from the outside by means of a setting piston.
In their positions corresponding to the pressureless condition of the hydraulic system, the chucking bolts apply against a stop of the jaws, through which the chucking force is directly transmitted from the jaw to the chucking bolt. With a balanced chucking, on the contrary, the chucking bolts are backed up in a floating manner and can adapt to the contour of the workpiece.
In this power chuck, it is possible to switch from one chucking mode to the other by means of a manually operated setting piston, however, the chuck is very expensive in manufacture. No economical production can be provided and the complicated construction with pressures up to 300 bar acting on the elastic seals necessarily entails disturbances in the manufacturing process. The primary drawback, however, is that the switching must always be effected with the chuck stopped, by manually setting the piston back and forth, to force the pressure fluid into the hydraulic system, or to produce a corresponding free space for the chucking bolts applying against the jaws.